The controlled organization of inorganic materials into multi-dimensional addressable arrays is the foundation for both logic and memory devices, as well as other nonlinear optical and sensing devices (Zhirnov et al., 2001, Computer 34, 34-43, Xia et al., 2000, Adv. Mater. 12, 693-713). Many of these devices are currently fabricated using lithographic patterning processes that have progressively developed toward greater integration densities and smaller sizes. At submicron scales, however, conventional lithographic processes are approaching their practical and theoretical limits. At scales below 100 nm, ion and electron beam lithography becomes prohibitively expensive and time consuming, and more importantly, at these scales quantum effects fundamentally change the properties of devices (Sato et al., 1997, J. Appl. Phys. 82, 696).
Nanoscale templates for constrained synthesis, in situ deposition, or direct patterning of nanometer scale inorganic arrays are being developed using both artificial and natural materials. Artificial materials such as microphase separated block copolymers (Park et al., 2001, Appl. Phys. Lett. 79, 257-259) and hexagonally close-packed spheres (Hulteen et al., 1995, J. Vac. Sci. Technol. A, 1553-1558) have been used for nanoscale fabrication. Natural materials such as DNA (Richter et al., 2000, Adv. Mater. 12, 507-510; Keren et al., 2002, Science 297, 72-75), bacterial and archaeal surface layer proteins (S-layer proteins) (Sleytr et al., 1999, Angew. Chem. Int. Ed. 38, 1034-1054; Douglas et al., Appl. Phys. Lett. 48, 676-678; Hall et al., 2001, CHEMPHYSCHEM 3, 184-186), virus capsids (Shenton et al., 1999, Adv. Mater. 11, 253-256; Douglas et al., 1999, Adv. Mater., 679-681; Douglas et al., Nature 393, 152-155; Wang et al., 2002, Angew. Chem. Int. Ed. 41, 459-462), phage (Lee et al., 2002, Science 296, 892-895), and some globular proteins (Yamashita, I., 2001, Thin Solid Films 393, 12-18) have been used as templates and in other nanoscale applications.
Various nanometer scale objects, including arrays of nanoparticles formed by non-conventional methods are being explored for use as viable alternatives to standard lithographically patterned devices. Individual nanoparticles, also known as quantum dots (QDs), have been shown to behave as isolated device components such as single electron transistors (Likharev, K. K., 1999, Proc. IEEE 87, 606-632; Thelander et al., 2001, Appl. Phys. Lett. 79, 2106-2108). Theoreticians have postulated that two-dimensional arrays of QDs with nanoscale resolution could form the basis of future generations of electronic and photonic devices. The function of these devices will be based on phenomena such as coulomb charging, inter-dot quantum tunneling and other coherent properties derived from the electronic consequences of confinement and nanoparticle surface area to volume ratios (Maier, S. A. et al., 2001, Adv. Mater. 13, 1501-1505; Maier et al., Phys. Rev. B 65, 193408; Zrenner, A. et al., 2002, Nature 418, 612-614; Berven et al., 2001, Adv. Mater. 13, 109-113).
Traditional techniques for patterning ordered arrays of materials onto inorganic substrates and manufacturing devices currently used are ion beam lithography and molecular beam epitaxy. These techniques possess inherent limitations due to the use of polymeric light masks for pattern formation, however, there is a theoretical limitation of patterning that could ultimately limit the processes in the hundreds of nanometers.
While there are strong incentives to develop nanoscale architectures, these developments require alternate fabrication methods and new insights into the behavior of materials on nanometer scales (Nalwa, H. S., 2000, Handbook of materials and nanotechnology, Academic Press, San Diego).